1. Technical Field
The present invention relates generally to a stator of an electric rotating machine such as an electric motor or an electric generator to be mounted in, for example, automotive vehicles such as electric vehicles or hybrid vehicles and a production method thereof.
2. Background Art
FIG. 1 illustrates a conventional stator 10 for use in electric rotating machines. The stator 10 includes an annular stator core 14 and a stator winding 16. The stator core 14, as illustrated in FIG. 2, has a plurality of slots 12 arrayed at regular intervals in a circumferential direction thereof. The stator winding 16 is wound through the slots 12 of the stator core 14. The stator winding 16 is made up of a plurality of U-shaped conductor segments 16a which are inserted into the slots 12, for example, from the lower side of FIG. 1. Ends 16b of the U-shaped conductor segments 16a extend outside an upper end, as viewed in FIG. 1, of the stator core 14 and are arrayed coaxially. Each of the ends 16b of the conductor segments 16a is bent in either of opposite circumferential directions of the stator core 14, so that every two of the ends 16b which belong to the different conductor segments 16a are arrayed adjacent each other in a radial direction of the stator core 14. Additionally, each of the U-shaped conductor segments 16a is twisted so that every two of the ends 16b of the U-shaped conductor segments 16a which are to be welded are arranged close to each other in the radial direction of the stator core 14 to form a coil end pair 16c. The coil end pairs 16c are, as can be seen from FIG. 3, arranged at regular intervals in the circumferential direction of the stator core 14 in coaxial circular lines and also aligned radially in a plurality of lines. In the illustrated example, the ten (10) coil ends 16b are arrayed above each of the slots 12 of the stator core 14.
The coil ends 16b of each pair 16c are joined into a weld 16d, as illustrated in FIG. 4, by, for example, TIG (Tungsten Inert Gas) welding. Such welding requires an interval d1 between every adjacent two of the coil end pairs 16c (i.e., the welds 16d) along the end surface of the stator core 14 to be great enough to ensure electric insulation therebetween.
The ten (10) coil ends 16b extend, as illustrated in FIG. 5, vertically from each of the slots 12 and are arrayed in line in the radial direction of the stator core 14. The coil ends 16b above each slot 12 will also be referred to as first to tenth coil ends 16b-1 to 16b-10, respectively, which are arrayed from inward to outward of the stator core 14. Such radial in-line arrangement of the coil ends 16b may result in a lack of an interval d1 between every adjacent two of the coil ends 16b required to ensure the electric insulation therebetween, which may result in undesirable electrical discharge when the coil ends 16b are welded.
In order to prolong the interval d1 between every adjacent two of the coil end pairs 16c, Japanese Patent First Publication No. 2004-32882 (corresponding to U.S. Pat. No. 6,833,648 B2, assigned to the same assignee as that of this application) discloses an arrangement of the coil ends 16b-1 to 16b-10, as illustrated in FIG. 6. Specifically, the third to tenth coil ends 16b-3 to 16b-10 are shaped to have base portions 16e slanting outward at gradually increasing angles.
The third to tenth coil ends 16b-3 to 16b-10 are bent radially outward of the stator core 14 to have the slant base portions 16e after which all the first to tenth coil ends 16b-1 to 16b-10 are bent, as illustrated in FIG. 1, in the circumferential direction of the stator core 14. Each of the slant base portions 16e is required to have a height h1 from the end surface of the stator core 14, which will result in an increase in overall height h2 of the coil ends 16b-1 to 16b-10. This leads to an increase in size of the stator 10 undesirably. The increased size of the stator 10 requires increasing the size of a motor housing in which the stator 10 is to be disposed, which will result in deterioration in mountability of the electric rotating machine in automotive vehicles.
Each of the conductor segments 16b is also required to have a length great enough to bent the base portion 16e both in the outward direction and in the circumferential direction of the stator core 14, thus resulting in an increase in material cost of the stator winding 16.